This invention relates to a thermal cut-off fuse which is used in an electric appliance incorporating a heat-generating element to serve the purpose of opening the electric circuit of the electric appliance when the ambient temperature of the appliance is elevated to a danger level.
One of the various types of thermal cut-off fuses uses a thermal pellet made of a thermally sensitive material which retains a solid state at temperatures not exceeding a fixed level and assumes a liquid state on being elevated to reach the fixed level. This thermal cut-off fuse substantially comprises a pair of terminals, a conductive, elastic contact member interposed between the two terminals, a thermal pellet adapted to remain in a solid state at normal room temperature and, by virtue of this solid state, restrain the elasticity of the contact member and, and thereby, establish electric continuity between the two terminals. When the ambient temperature of this fuse is elevated to the danger level, the thermal pellet melts and releases the contact member from the restrained elasticity. Consequently, the contact member severs the electric continuity between the two terminals to fulfill the purpose of the fuse.
The conventional thermal cut-off fuse of such a construction has a possibility of being accidentally brought into the state of broken electric continuity such as on exposure to external impulses or in consequence of degradation of elasticity because the contact member serving to establish the electric continuity between the terminals relies for its perfect contact upon the elasticity of its own material. Further because of the requirement that the area in which such a contact is made should be minimized to ensure improved sensitivity of the contact motion, the fuse suffers from a high contact resistance and tends to provide inferior efficiency for use as an element in the electric circuit. Generally thermal cut-off fuses of an ordinary run are required to be available in a small size of the order of 5 mm in diameter and 1 cm or less in length, so that they inevitably entail a drawback that the assembly of their minute component parts necessitates high skill on the part of workers.
An object of the present invention is to provide a thermal cut-off fuse which enjoys high accuracy of response to the fixed temperature level, possesses an ability to assume the state of a broken electric continuity without fail, offers no appreciable resistance of contact and enjoys simplicity of fabrication.